Communication of data between remotely-positioned sending and receiving stations is a necessary adjunct of modern society. A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of data between the sending and receiving stations.
Advancements in communication technologies have permitted the development, and commercial implementation, of new types of communication systems. Radio communication systems are exemplary of communication systems which have benefited from the advancements in communication technologies. Improvements to existing types of radio communication systems as well as new types of radio communication systems have been made possible as a result of such advancements.
Modern wireless radio communication systems inherently permit increased communication mobility in contrast to the use of conventional wire line communication systems only. Communication channels between sending and receiving stations of a radio communication system are established via radio links formed therebetween. The communication channels are referred to as radio channels and do not require fixed connections for their formation.
The advancements in communication technologies include, for instance, the use of digital communication techniques. The use of digital communication techniques enables an increase in the communication capacity of a communication system, as well as an improvement in the quality levels of communications effectuated in the communication system.
Information to be communicated in a digital communication system is digitized. Once digitized, the digitized information is formatted, such as into data packets, and converted into a form to permit its communication upon the communication channel. In an ideal communication system, the data packets, subsequent to transmission upon the communication channel and reception at a receiving station, are essentially identical to the corresponding data packets prior to their communication upon the communication channel. In an actual communication system, however, distortion is introduced upon the data during its communication upon the communication channel such that the values of the representations of the data, when received at the receiving station, differ, in part, with the corresponding values of the data packets prior to its communication upon the communication channel. If the amount of distortion is significant, the informational content of the data cannot accurately be recovered at the receiving station.
Multipath transmission, for instance, causes fading of the received data energy. Such fading might alter the values of the symbols in a data packet, during transmission upon the communication channel. Quasistatic flat fading, for example, models a situation in which fading is flat in frequency and is constant over the duration of a relevant block of transmitted signals. In contrast, fast flat fading models a situation in which fading is flat in frequency but may change as fast as from a transmitted symbol epoch to a subsequent epoch. If the propagation distortion is not properly corrected, resultant communication quality levels of the communications are, at a minimum, reduced.
Various techniques are utilized to compensate for the distortion introduced upon the data as a result of communication of the data upon a non-ideal communication channel. Increasing the diversity of the data is utilized, for instance, to increase the likelihood that the informational content of the data can be recovered.
Redundancy in time of the data, prior to its communication, is referred to as creating time diversity. Encoding increases the redundancy of the data. Because of the increased redundancy, loss of portions of the data due, for example, to fading is less likely to prevent the recovery of the informational content of the data.
Space diversity is also utilized to compensate for distortion. Typically, space diversity refers to the utilization of more than one transmit antenna at a sending station at which to transduce the data. The antenna transducers are separated by distances great enough to ensure that the data communicated from the respective transducers fade in an uncorrelated manner. Fading of the data transmitted upon one propagation path to a receiving station is thereby less likely to fade in the same manner and at the same time as data communicated to a receiving station upon a different propagation path.
Space and time diversity are sometimes utilized together, thereby further to enhance diversity and better combat the signal fading caused, e.g., by multipath transmission.
Various coding techniques have been developed for use in transmit diversity schemes. Space-time codes have been developed to achieve diversity when transmitted upon fading channels by implementing redundancy at a sending station in both space and time. Systematic and recursive codes have also been developed. Systematic and recursive codes are advantageous in that parallel concatenation can be performed when data encoded in such manner is communicated. However, systematic and recursive, true space-time codes have generally not been available; systematic and recursive codes for transmit diversity have been obtained by straightforward extensions of, e.g., classical convolutional codes. If an improved, structured manner could be provided by which to form a systematic, recursive, space-time code, parallel concatenation of space-time codes could be performed in order to obtain richer configurations.
It is in light of this background information, related to communication of data upon a channel susceptible to fading, that the significant improvements of the present invention have evolved.